Peter Frost's anthropology blog, with special reference to sexual selection and the evolution of skin, hair, and eye pigmentation

Saturday, January 26, 2013

When was the split?

Genetic data suggest that ancestral East Asians
diverged from ancestral Europeans long after the African/non-African split
(source). This timeline, however, seems to be challenged by archaic DNA that is
reputed to be 40,000 years old.

When did the ancestors of Europeans and East Asians
part company? In my opinion, the divergence must have happened long after the
time (c. 50,000 BP) when modern humans began to spread out of Africa. It
probably occurred near the onset of the last ice age (25,000 – 10,000 BP), when
advancing ice sheets and glacial lakes restricted gene flow between the western
and eastern ends of Eurasia (Rogers, 1986).

This timeline is supported by several pieces of
evidence:

1. Human skin began to lighten some 30,000 years ago
in a population that was ancestral to both Europeans and East Asians (Beleza et
al., 2012). A second phase of skin lightening, which affected only Europeans,
occurred between 19,000 and 13,000 years ago. Proto-Eurasians must have
therefore begun to diverge into two groups somewhere between 30,000 BP and
19,000 BP.

2. A Y-chromosome study suggests that all North
Eurasian peoples descend from a common ancestral population dated to about
15,000 BP (Stepanov & Puzyrev, 2000; see also Armour et al., 1996; Santos
et al., 1999; Zerjal et al., 1997).

3. The language families of northern Eurasia,
particularly Uralic and Yukaghir and more generally Uralic-Yukaghir,
Eskimo-Aleut, Chukotko-Kamchatkan and Altaic, share deep structural affinities
that point to a common origin and not simply to word borrowing (Cavalli-Sforza,
1994, pp. 97-99; Fortescue, 1998; Rogers, 1986).

4. Archeological evidence (characteristic lithic
technology, grave goods with red ocher, and sites with small shallow basins)
shows the presence of a common cultural tradition throughout Europe and Siberia
20,000 to 15,000 years ago (Goebel, 1999; Haynes, 1980; Haynes, 1982).

Nonetheless, this timeline now seems disproved by a
recent study of archaic DNA:

We have extracted DNA from a
40,000-y-old anatomically modern human from Tianyuan Cave outside Beijing,
China. […] The nuclear DNA sequences determined from this early modern human
reveal that the Tianyuan individual derived from a population that was
ancestral to many present-day Asians and Native Americans but postdated the divergence
of Asians from Europeans. (Fu et al., 2013)

So ancestral Europeans and East Asians had already
begun to diverge from each other by 40,000 BP. Considering that modern humans
entered the Middle East around 46-47,000 BP, the time of divergence must have
been close to the initial split between Africans and non-Africans (Schwarcz et
al., 1979). Yet the genetic data argue otherwise.

When a new finding seems inconsistent with other
data, one should take a second look. Do those human remains from Tianyuan Cave
really date back to 40,000 years ago? Actually, they were initially dated to
25,000 BP, by means of uranium series dating of deer teeth from the same cave
layer (Tong et al., 2004). Because this dating method is considered problematic
when applied to organic remains, radiocarbon dating was later used to get a
firmer date, which turned out to be 39,000 – 42,000 BP (Shang et al., 2007).

The two dating methods differed by 15,000 years.
That’s a big discrepancy, and it may be why Shang et al. (2007) repeated their
radiocarbon dating on several organic remains from the same layer. Such an
approach, however, doesn’t rule out the possibility of a shared source of
error, either in the remains themselves or in the testing laboratory.

There are two other reasons for doubting the
estimate of 40,000 BP:

Associated
faunal remains

The modern human remains from layer III were
associated with the remains of other fauna. In general, the faunal assemblage
indicates a significantly colder climate than the one that now prevails around
Beijing. On the one hand, layer III had remains of the Siberian musk deer (Moschus moschiferus), which now lives
farther north in the taiga of southern Siberia and northern Manchuria. On the
other hand, layer III had no remains of warm climate species, i.e., the rhesus
macaque (Macaca mulatta) and the
masked palm civet (Paguma larvata),
even though these species were present in the uppermost Holocene layer (Shang
et al., 2007). The faunal evidence is thus consistent with the colder climate
that existed when the last ice age began 25,000 years ago. It is not consistent
with the warmer climate that prevailed 40,000 years ago in southern Siberia and
northern China during the Malokheta Interstade of the Karga Interglacial
(33,000 - 43,000 BP). At that time, average annual temperatures were as much as
2-3° C warmer than they are today (Goebel, 2004).

An outlier among
finds of early East Asians

With a dating of 40,000 BP, these remains are much
older than all other known finds that might be ancestral to present-day East
Asians. The oldest rivals to Tianyuan Cave are Yamashita-cho, Okinawa (≈32,000
BP), Zhoukoudian Upper Cave, China (24,000 – 29,000 BP), Pinza-Abu, Okinawa ( ≈26,000
BP), and Minatogawa, Okinawa (≈18,000 BP) (Shang et al., 2007).

Conclusion

Archaic DNA promises to revolutionize our
understanding of human origins. Unfortunately, it may also confer an aura of
false certainty on new findings, thereby discouraging the healthy skepticism
that makes good science possible. The Tianyuan Cave remains are undoubtedly
those of an early East Asian and thus promise to shed much light on the
beginnings of this branch of humanity. There are, however, reasons for doubting
the date of 40,000 BP, and such doubts will probably become more insistent as
we retrieve archaic DNA from other East Asian remains.

"Chinese scientists are prone to claiming that the there is continuity of humans in China as far back as you can go"

Yes, and it's pretty much the opposite of the funded occidental researcher, who is lobbied to find that 'europeans' never existed and were initially transposed africans. My bet is that, deep inside, and despite the appearences given for the occidental medias, chinese evolutionists are not darwinian by essence. Darwinism as a causal force is completely antithetic of confusianism, boudhism or even chamanism.

Western scientists' involvement is no guarantee of objectivity. Note the claim (once widely accepted) that there was use of fire by Peking man for lighting, cooking, and heating at Zhoukoudian 400,000 years ago.

This is basically as old as Cro magnon.So, 'differentiated from europeans'? but what europeans?

Hypothesis number 1:African Hunters looking more or less like Buhmen (with asian traits) reach Eurasia and loose all their afro-asian features to become european-like Cro Magnons. Once in Asia these cro-magnons reacquire asian features and loose their european features.

Or hypothesis number 2:African Hunters looking more or less like Buhmen reach Eurasia but DO NOT loose their afro-asian features immediately, so Cro Magnons must have looked partly like robust afro-asian or Bushmen. 40 000 years ago, some of them move in Asia where these loose some African features but retain the bushmen-asian features, while those who stayed in Europe loose both their African Bushman and asian features.

In hypothesis 2 nothing is lost then reacquired, and this is much more economic than hyp. 1) so the so-called 'europeans Cro-Magnons' must have looked like robust Bushmen more than Europeans.

I retouched a picture of a San Buhsman from Africa to show how these "Africans' actually look more asian or amerindian than African. I choose a Thai man by comparison and a reconstruction of a 11500 years old south amerindian from Wikipedia.

"Stable isotope dietary analysis of the Tianyuan 1 early modern human' says it lived on fish for a substantial part of the year; which could only be due to scarcity of animals to hunt, yet the area was swarming with game during the Malokheta Interstade."

If you look at it from the point of view of food-getting then there are three options- gathering- hunting- fishing

Early humans who developed fishing might have been able to expand much faster than the others as long as they stuck to coasts and rivers.

In terms of out of africa that gives two dramatically different and divergent routes: a southern coastal one and an atlantic one - with possible later hunter and/or gatherer expansions as they caught up.

...my point was that asians did not differentiate from europeans, since there were no true europeans at that time. They differentiated from asian-like africans who lived in Europe.

Also, what is PNG in the figure? Anyway, i scooped the article quickly but notice that the authors clearly state in Table4 that Neanderthals are closer to europeans (non africans) than Africans. So reciproquely, Europeans are closer to Neanderthals than Africans.Since we consider Neanderthals a separate sub species of homo sapiens, that makes Africans an even more separate sub species.

Welcome to my blog! For the most part, this page will be an extension of my website, with comments relating to my research. But it will also branch out into more general discussions of human evolution.